1. Field of the Invention
One disclosed aspect of the embodiments relates to an image capturing apparatus including a focus detection unit using a contrast evaluation value and an image capturing method.
2. Description of the Related Art
Japanese Patent No. 4,536,248 discusses a focus detection apparatus configured to detect a focal position while performing contrast evaluation on a plurality of predetermined focal point detection areas. The focus detection apparatus performs face detection and limits focal point detection areas according to the position of the detected face.
The focus detection apparatus discussed in Japanese Patent No. 4,536,248 has first and second focusing control modes. In the first focusing control mode, a human eye area is intensively and selectively set as a focal point detection area. In the second focusing control mode, the focus detection apparatus performs focus detection using autofocus (AF) control that is different from the first focusing control mode.
In the focus detection, first, for example, an image area such as a screen center is targeted as a focal point detection area, and focus control is performed on the image area in the second focusing control mode. Then, after the focus control is performed on an area near an focusing position, an eye area is targeted as a focal point detection area, and the focus control is performed on the eye area in the first focusing control mode, whereby the focus is controlled onto a final focusing position. By the foregoing operation, the face especially the eyes can be focused.
Further, Japanese Patent No. 4,974,812 discusses an image capturing apparatus that focuses on a specific object such as a face without being disturbed by a background subject. In Japanese Patent No. 4,974,812, there are first and second areas. In the first area, a focal point detection area is set to cover a contour of a specific object such as a face. In the second area, a focal point detection area that is smaller than the first area is set inside the contour of the specific object.
In each of the first and second areas, spatial frequency components of a plurality of bands in the focal point detection areas are detected. If a difference between the bands of the spatial frequency components detected in the first area is larger than that in the second area, there may be a possibility of perspective conflict, so that the range of focus movement for the focus detection is limited to be narrow. The foregoing operation is performed so that if a perspective conflict is detected between the specific object and the background subject, the range of focus movement for the focus detection is limited to be narrow enough to exclude the background, whereby the perspective conflict can be avoided.
In the case of the image capturing apparatus discussed in Japanese Patent No. 4,536,248, if the shooting distance is long, the size of a face sometimes becomes so small that an image of an eye area is shot in significantly small size. In this case, it is sometimes impossible to detect a sufficient contrast, which results in focus determination at a wrong focusing position when making a focus determination or makes the focusing impossible. This problem becomes especially conspicuous under the conditions such as backlight and overexposure/underexposure that make the contrast evaluation difficult.
In the image capturing apparatus discussed in Japanese Patent No. 4,974,812, a wide focal point detection area is set to cover a contour of a specific object such as a face. If the focal point detection area is set in such a way, the focal point detection area is likely to include subjects showing various exposure amounts such as a face and a background. As a result, the contrast of a main subject is not sufficiently obtained, making it impossible to detect a focal point with high precision.